Control of polishing of multiple substrates on the same platen in chemical mechanical polishing

ABSTRACT

A polishing method includes positioning two substrates in contact with the same polishing pad. Prior to commencement of polishing and while the two substrates are in contact with the polishing pad, two starting values are generated from an in-situ monitoring system. Either a starting polishing time or a pressure applied to one of the substrates can be adjusted so that the two substrates have closer endpoint conditions. During polishing the two substrates are monitored with the in-situ monitoring system to generate a two sequences of values, and a polishing endpoint can be detected or an adjustment for a polishing parameter can be based on the two sequences of values.

TECHNICAL FIELD

The present disclosure relates generally to chemical mechanical polishing of multiple substrates.

BACKGROUND

An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of a patterned layer is exposed. A conductive filler layer, for example, can be deposited on a patterned insulative layer to fill the trenches or holes in the insulative layer. After planarization, the portions of the conductive layer remaining between the raised pattern of the insulative layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. For other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness is left over the non planar surface. In addition, planarization of the substrate surface is usually required for photolithography.

Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier head. The exposed surface of the substrate is typically placed against a rotating polishing pad with a durable roughened surface. The carrier head provides a controllable load on the substrate to push it against the polishing pad. A polishing liquid, such as a slurry with abrasive particles, is typically supplied to the surface of the polishing pad.

In some chemical mechanical polishing systems, multiple substrates are polished simultaneously on the same polishing pad. However, existing polishing techniques in such polishing systems may not satisfy increasing demands of semiconductor device manufacturers.

SUMMARY

In some semiconductor fabrication processes, the starting thickness of the layer being polished can differ from substrate-to-substrate, even for substrates from the same lot or cassette. As a consequence, for a polishing system in which multiple substrates are polished simultaneously on the same polishing pad, the multiple substrates can have different starting layer thicknesses. Moreover, for some fabrication situations, the starting thickness for each substrate may not be known, e.g., there may not be in-line measurement of the pre-polishing layer thickness. In addition, even if the polishing rate for the one of the substrates is adjusted based on in-situ measurements, variations in when the substrates reach their target thickness can still occur. On the one hand, if polishing is halted simultaneously for the substrates, then one or more substrates will not be at the desired thickness. On the other hand, if polishing for the substrates is stopped at different times, then some substrates may have defects and the polishing apparatus may be operating at lower throughput.

One technique is to measure the pre-polish thickness of the layer being polished with an in-situ monitoring system. Either the starting polishing time or the pressure applied to the substrates can be adjusted so that the substrates have closer endpoint conditions.

In one aspect, a polishing method includes positioning a first substrate and a second substrate in contact with the same polishing pad, prior to commencement of polishing and while the first substrate and second substrate are in contact with the polishing pad generating from an in-situ monitoring system a first starting value and a second starting value from the first substrate and the second substrate respectively, calculating an adjusted first pressure for the first substrate, polishing the first substrate on the polishing pad with the adjusted pressure and polishing the second substrate on the polishing pad with a second pressure, monitoring the first substrate and the second substrate during polishing with the in-situ monitoring system to generate a first sequence of values for the first substrate and a second sequence of values for the second substrate, and at least one of detecting a polishing endpoint for the first substrate and the second substrate or determining an adjustment for a polishing parameter based on the first sequence of values and the second sequence of values.

Implementations may include one or more of the following features. Determining the adjusted first pressure may include multiplying a default pressure by a ratio based on the first starting value and the second starting value. The default pressure may be a preset pressure or a pressure dynamically calculated based on monitoring of a prior substrate. The adjusted first pressure P_(ADJ1) may be set to P_(DEF1)*(TV−V2)/(TV−V1), where TV is a target value, V1 is the first starting value, V2 is the second starting value, and P_(DEF1) is the default pressure. The polishing endpoint may be detected. Detecting the polishing endpoint may include fitting a first function to the first sequence of values and determining a time at which the first function equals the target value, or fitting a second function to the second sequence of values and determining a time at which the second function equals the target value. The in-situ monitoring system may include an eddy current monitoring system, and polishing the first substrate may include polishing a first metal layer on the first substrate and polishing the second substrate may include polishing a second metal layer on the second substrate. The in-situ monitoring system may include a spectrographic monitoring system, and wherein polishing the first substrate comprises polishing a first dielectric layer on the first substrate and polishing the second substrate comprises polishing a second dielectric layer on the second substrate. The first substrate may be the substrate having a thicker layer to be polished, or the first substrate may be the substrate having a thinner layer to be polished.

In another aspect, a polishing method includes positioning a first substrate and a second substrate in contact with the same polishing pad, prior to commencement of polishing and while the first substrate and second substrate are in contact with the polishing pad generating from an in-situ monitoring system a first starting value and a second starting value from the first substrate and the second substrate respectively, calculating a delay time for the second substrate based on the first starting value and the second starting value, polishing the first substrate on the polishing pad, after the delay time from commencing polishing of the first substrate polishing the second substrate on the polishing pad, monitoring the first substrate and the second substrate during polishing with the in-situ monitoring system to generate a first sequence of values for the first substrate and a second sequence of values for the second substrate, and at least one of detecting a polishing endpoint for the first substrate and the second substrate or determining an adjustment for a polishing parameter based on the first sequence of values and the second sequence of values.

Implementations can include one or more of the following features. The delay time may be set to a difference between the first starting value and the second starting value divided by a default polishing rate. The default polishing rate may be a preset polishing rate or a polishing rate dynamically calculated based on monitoring of a prior substrate. The delay time ΔT may be set to (V2−V1)/R, where V1 is the first starting value, V2 is the second starting value, and R is the default polishing rate. The polishing endpoint may be detected. Detecting the polishing endpoint may include fitting a first function to the first sequence of values and determining a time at which the first function equals the target value, or fitting a second function to the second sequence of values and determining a time at which the second function equals a target value. The in-situ monitoring system may include an eddy current monitoring system, and wherein polishing the first substrate may include polishing a first metal layer on the first substrate and polishing the second substrate may include polishing a second metal layer on the second substrate. The in-situ monitoring system may include a spectrographic monitoring system, and wherein polishing the first substrate may include polishing a first dielectric layer on the first substrate and polishing the second substrate may include polishing a second dielectric layer on the second substrate. The second substrate may be the substrate having a thinner layer to be polished. In other aspects, polishing systems and computer-program products tangibly embodied on a computer readable medium are provided to carry out these methods.

Certain implementations may have one or more of the following advantages. Substrates polished simultaneously on the same polishing pad may reach their target thickness closer to the same time (or if polishing is halted simultaneously, then the substrates can have closer to the same thickness). If the in-situ monitoring system is used to adjust the polishing rate during polishing, the adjustments it needs to make may be smaller, which may make the in-situ monitoring system more effective. Defects, such as scratches caused by rinsing a substrate with water too early or corrosion caused by failing to rinse a substrate in a timely manner, may be reduced, and substrate-to-substrate thickness uniformity may be improved.

The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic cross-sectional view of an example of a polishing apparatus having two polishing heads.

FIG. 2 illustrates a schematic top view of a substrate having multiple zones.

FIG. 3A illustrates a top view of a polishing pad and shows locations where in-situ measurements are taken on a first substrate.

FIG. 3B illustrates a top view of a polishing pad and shows locations where in-situ measurements are taken on a second substrate.

FIG. 4A illustrate expected polishing rates for a first implementation.

FIG. 4B illustrate expected polishing rates for a second implementation.

FIG. 5 illustrates a plurality of traces for different substrates.

FIG. 6 illustrates a calculation of a desired slope for a substrate based on a time that a function fit to a trace reaches a target value.

FIG. 7 illustrates a calculation of times that a plurality of substrates reach a target value.

FIG. 8 is a flow diagram of an example process for adjusting the polishing of a plurality of substrates.

Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

Where multiple substrates are being polished simultaneously, e.g., on the same polishing pad, differences in the starting thickness of the layer being polished can lead to the substrates reaching their target thickness at different times. By determining the starting thickness with an in-situ polishing system before polishing commences, a polishing start time or a polishing rate for at least one of the substrates can be adjusted so that the substrates achieve closer endpoint conditions. By “closer endpoint conditions,” it is meant that the substrates would reach their target thickness closer to the same time than without such adjustment, or if the substrates halt polishing at the same time, that the substrates would have closer to the same thickness than without such adjustment.

FIG. 1 illustrates an example of a polishing apparatus 100 for polishing a plurality of substrates 10. Each substrate can be, for example, a product substrate (e.g., which includes multiple memory or processor dies), a test substrate, a bare substrate, and a gating substrate. The substrate can be at various stages of integrated circuit fabrication, e.g., the substrate can be a bare wafer, or it can include one or more deposited and/or patterned layers. The term substrate can include circular disks and rectangular sheets.

The polishing apparatus 100 includes a rotatable disk-shaped platen 120 on which a polishing pad 110 is situated. The platen is operable to rotate about an axis 125. For example, a motor 121 can turn a drive shaft 124 to rotate the platen 120. The polishing pad 110 can be detachably secured to the platen 120, for example, by a layer of adhesive. The polishing pad 110 can be a two-layer polishing pad with an outer polishing layer 112 and a softer backing layer 114.

The polishing apparatus 100 can include a dispenser 130 operable to dispense a polishing liquid 132, such as an abrasive slurry, onto the polishing pad 110. The polishing apparatus can also include a polishing pad conditioner to abrade the polishing pad 110 to maintain the polishing pad 110 in a consistent abrasive state.

The polishing apparatus 100 includes two (or two or more) carrier heads 140. Each carrier head 140 is operable to hold a substrate 10 (e.g., a first substrate 10 a at a first carrier head 140 a and a second substrate 10 b at a second carrier head 140 b) against the polishing pad 110, i.e., the same polishing pad. Each carrier head 140 can have independent control of the polishing parameters, for example pressure, associated with each respective substrate.

In particular, each carrier head 140 can include a retaining ring 142 to retain the substrate 10 below a flexible membrane 144. Each carrier head 140 also includes a plurality of independently controllable pressurizable chambers defined by the membrane, e.g., three chambers 146 a-146 c, which can apply independently controllable pressurizes to associated zones 148 a-148 c on the flexible membrane 144 and thus on the substrate 10 (see FIG. 2). Referring to FIG. 2, the center zone 148 a can be substantially circular, and the remaining zones 148 b-148 e can be concentric annular zones around the center zone 148 a. Although only three chambers are illustrated in FIGS. 1 and 2 for ease of illustration, there could be one chamber, two chambers, or four or more chambers, e.g., five chambers.

Returning to FIG. 1, each carrier head 140 is suspended from a support structure 150, e.g., a carousel or track, and is connected by a drive shaft 152 to a carrier head rotation motor 154 so that the carrier head can rotate about an axis 155. Optionally each carrier head 140 can oscillate laterally, e.g., on sliders on the carousel or track 150; or by rotational oscillation of the carousel itself. In operation, the platen is rotated about its central axis 125, and each carrier head is rotated about its central axis 155 and translated laterally across the top surface of the polishing pad.

While only two carrier heads 140 are shown, more carrier heads can be provided to hold additional substrates so that the surface area of polishing pad 110 may be used efficiently. Thus, the number of carrier head assemblies adapted to hold substrates for a simultaneous polishing process can be based, at least in part, on the surface area of the polishing pad 110.

The polishing apparatus also includes an in-situ monitoring system 160, which can be used to determine an initial thickness of the layer each substrate before polishing commences. The in-situ monitoring system 160 can also be used to detect a polishing endpoint, or to determine whether to adjust a polishing rate or an adjustment for the polishing rate, as discussed below. Prior to polishing, for each substrate the in-situ monitoring system 160 generates a value that depends on the pre-polishing thickness of the layer on that substrate. During polishing, for each substrate, the in-situ monitoring system generates a time-varying sequence of values that depends on the thickness of a layer on that substrate.

For example, the in-situ-monitoring system 160 be an eddy current monitoring system. An eddy current monitoring system can generate a signal that depends on the thickness of a metal layer on the substrate. Eddy current monitoring systems are described in U.S. Pat. No. 6,924,641 and U.S. Pat. No. 7,112,960, each of which is incorporated by reference. For some fab systems, the incoming thickness of a metal layer on the substrate is difficult to control; in this case the eddy current monitoring system can be particularly useful.

As another example, the in-situ-monitoring system 160 can be an optical monitoring system. In particular, the optical monitoring system 160 can be a spectrographic monitoring system that measures a sequence of spectra of light reflected from a substrate during polishing. One monitoring technique is, for each measured spectrum, to identify a matching reference spectrum from a library of reference spectra. Each reference spectrum in the library can have an associated characterizing value, e.g., a thickness value or an index value indicating the time or number of platen rotations at which the reference spectrum is expected to occur. By determining the associated characterizing value for each matching reference spectrum, a time-varying sequence of characterizing values can be generated. This technique is described in U.S. Patent Publication No. 2010-0217430, which is incorporated by reference. Another monitoring technique is to track a characteristic of a spectral feature from the measured spectra, e.g., a wavelength or width of a peak or valley in the measured spectra. The wavelength or width values of the feature from the measured spectra provide the time-varying sequence of values. This technique is described in U.S. Patent Publication No. 2011-0256805, which is incorporated by reference. Another monitoring technique is to fit an optical model to each measured spectrum from the sequence of measured spectra. In particular, a parameter of the optical model is optimized to provide the best fit of the model to the measured spectrum. The parameter value generated for each measured spectrum generates a time-varying sequence of parameter values. This technique is described in U.S. Patent Application No. 61/608,284, filed Mar. 8, 2012, which is incorporated by reference.

Another monitoring technique is to perform a Fourier transform of each measured spectrum to generate a sequence of transformed spectra. A position of one of the peaks from the transformed spectrum is measured. The position value generated for each measured spectrum generates a time-varying sequence position values. This technique is described in U.S. patent application Ser. No. 13/454,002, filed Apr. 23, 2012, which is incorporated by reference.

The in-situ monitoring system 160 includes a sensor 162 that is supported by and rotates with the platen 120. In this case, the motion of the platen will cause the sensor 162 to scan across each substrate. The sensor 162 can be supported by a removable module 168 that fits in a recess 128 in the top surface of the platen 120.

As shown by in FIG. 3A, due to the rotation of the platen (shown by arrow 204), as sensor 162 travels below the first carrier head 140 a, the sensor 162 can make measurements at positions 201 below the first substrate 10 a. This permits the monitoring system 160 to generate a signal with a value that depends on the thickness of the layer of the substrate 10 a. Similarly, as shown by in FIG. 3B, due to the rotation of the platen, as the sensor 162 travels below the second carrier head, the sensor 162 can make measurements at positions 202 below the second substrate 10 b. This permits the monitoring system 160 to generate a signal with a value that depends on the thickness of the layer of the substrate 10 b.

Thus, for any given rotation of the platen, based on timing, motor encoder and/or platen position sensor information, the controller 190 can determine which substrate, e.g., substrate 10 a or 10 b, is the source of the signal. The number of positions 201, 202 shown in FIGS. 3A and 3B is illustrative, and depends on the sampling rate for the sensor 162. Over multiple rotations of the platen 120, for each substrate, a sequence of values can be obtained over time.

When the substrates 10 are initially lowered into contact with the polishing pad, the monitoring system 160 makes an initial measurement of each substrate. The initial measurements can provide a starting value for each substrate, e.g., values V1 and V2 for substrates 10 a and 10 b, respectively.

The initial measurements can be conducted under conditions in which effectively no polishing is occurring. For example, the measurements can be performed before slurry is supplied to the polishing pad, and before the carrier heads 140 apply a positive pressure to the substrates 10.

Based on the starting values V1 and V2, the controller 190 adjusts the polishing recipe to compensate for the difference in starting thickness of the layer on the substrate. In some implementations, the controller 190 determines a difference in polishing pressure to be applied to the substrates 10 a, 10 b by the carrier heads 140. In some implementations, the controller 190 determines a difference in starting time for application of pressure to the substrates 10 a, 10 b by the carrier heads.

FIG. 4A illustrates the progress of polishing where the controller 190 determines a difference in polishing pressure to be applied to the substrates 10 a, 10 b by the carrier heads 140. In particular, the pressure applied by at least one of the carrier heads 10 a, 10 b is adjusted from its default value to compensate for the difference in starting thickness so that the substrates have closer endpoint conditions. The default value can be a pressure that is preset by a recipe, or a pressure that has been computed by a process control module to account for environmental factors based on the polishing rate of a prior substrate.

For example, assuming that the starting values measured by the monitoring system 160 for the substrates 10 a, 10 b are V1 and V2, then the adjusted pressure P_(ADJ1) for the first substrate 10 a can be calculated as

P _(ADJ1) =P _(DEF1)*(TV−V2)/(TV−V1)

where TV is the target value for substrates 10 a and 10 b, and P_(DEF1) is the default polishing pressure for the substrate 10 a.

In FIG. 4A, the lines 190, 192 represent the expected progress of polishing of the substrates 10 a, 10 b, without any adjustment and under the assumption that the substrates 10 a, 10 b would have similar polishing rates (shown by the slopes of lines 190, 192, respectively). With the adjustment, the polish rate of the substrate 10 a changes, resulting in the expected progress of polishing of the substrate 10 a shown by line 194. The expected progress 194 of substrate 10 a should intersect the target value TV closer to the expected progress 192 of the substrate 10 b than the expected progress 190 without the adjustment.

FIG. 4B illustrates the progress of polishing where the controller 190 determines a difference in starting time for application of polishing pressure to the substrates 10 a, 10 b by the carrier heads 140. In particular, application of pressure to at least one of the carrier heads 10 a, 10 b is delayed from the start time to compensate for the difference in starting thickness so that the substrates have closer endpoint conditions. Thus, at the beginning of the polishing process, pressure is applied by one of the carrier heads, e.g., the carrier head 10 a, but pressure is not applied by the other carrier head, e.g., the carrier head 10 b, until expiration of a delay time AT. The delay time AT can be calculated based on the difference between the start values of the substrates 10 a, 10 b and a polishing rate. The polishing rate can be a default value, or a dynamic value that has been computed by a process control module to account for environmental factors based on the polishing rate of a prior substrate.

For example, assuming that the starting values measured by the monitoring system 160 for the substrates 10 a, 10 b are V1 and V2, then the delay time ΔT for the second substrate 10 b can be calculated as

ΔT=(V2−V1)/R

where R is the polishing rate for substrate 10 a.

In FIG. 4B, the lines 190, 192 represent the expected progress of polishing of the substrates 10 a, 10 b, without any adjustment and under the assumption that the substrates 10 a, 10 b would have similar polishing rates (shown by the slopes of lines 190, 192, respectively). With the delay time ΔT, the onset of polishing of the second substrate 10 b is delayed, resulting in the expected progress of polishing of the substrate 10 b shown by line 196. The expected progress 196 of substrate 10 b should intersect the target value TV closer to the expected progress 190 of the substrate 10 a than the expected progress 192 without the adjustment.

Referring to FIG. 5, once polishing commences, .e.g., slurry is provided to the polishing pad 110, the platen 120 is rotating, and pressure is being applied to at least one of the substrates 10 a or 10 b, the in-situ monitoring system 160 generates a time-varying sequence of values for each substrate. This sequence of values can be termed a trace. For example, a first sequence 210 of values 212 (shown by hollow circles) can be generated for the first substrate 10 a, and a second sequence 220 of values 222 (shown by solid circles) can be generated for the second substrate 10 b.

In general, for a polishing system with a rotating platen, each trace can include one, e.g., exactly one, value per sweep of the sensor below the substrate. If multiple zones on a substrate are being monitored, then there can be one value per sweep. Multiple measurements below the substrate can be combined to generate a single value that is used for control of the endpoint and/or pressure. However, it is also possible for more than one value to be generated per sweep of the sensor 162.

For each trace 210, 220, a polynomial function of known order, e.g., a first-order function (e.g., a line) is fit to the sequence of values for the associated substrate, e.g., using robust line fitting. For example, a first line 214 can be fit to the values 212 for the first substrate, and a second line 224 can be fit to the values 222 of the second substrate. Fitting of a line to the sequence of values can include calculation of the slope S of the line and an x-axis intersection time T at which the line crosses a starting value, e.g., 0.

Referring to FIG. 6, at some point during the polishing process, e.g., at a time T0, a polishing parameter for at least one substrate is adjusted to adjust the polishing rate the substrate such that at a polishing endpoint time, the plurality of substrates are closer to their target thickness than without such adjustment. In some embodiments, the plurality of substrates can have approximately the same thickness at the endpoint time.

In some implementations, one substrate is selected as a reference substrate, and a projected endpoint time TE at which the reference substrate will reach a target value V is determined. For example, as shown in FIG. 6, the first substrate 10 a is selected as the reference substrate, although a different substrate could be selected. The target value V is set by the user prior to the polishing operation and stored.

In order to determine the projected time at which the reference substrate will reach the target value, the intersection of the line of the reference substrate, e.g., line 214, with the target value, V, can be calculated. Assuming that the polishing rate does not deviate from the expected polishing rate through the remainder polishing process, then the sequence of values should retain a substantially linear progression. Thus, the expected endpoint time TE can be calculated as a simple linear interpolation of the line to the target value V, e.g., V=S·(TE−T).

The substrates other than the reference substrate can be defined as adjustable substrates. Where the lines for the adjustable substrates meet the expected endpoint time TE define projected endpoint for the adjustable substrate. The linear function of each adjustable substrate, e.g., line 224 in FIG. 6, can thus be used to extrapolate the estimated value, e.g., E2, that will be achieved at the expected endpoint time ET for the associated substrate. For example, the second line 224 can be used to extrapolate the expected value, E2, at the expected endpoint time ET for the second substrate.

As shown in FIG. 6, if no adjustments are made to the polishing rate of any of the substrates after time T0, then if endpoint is forced at the same time for all substrates, then each substrate can have a different thickness. Here, for example, the second substrate (shown by line 224) would endpoint at an expected value E2 greater (and thus a thickness less) than the expected value of the first substrate. Alternatively, if endpoint is forced for each substrate individually based on when the function equals the target value, each substrate could have a different endpoint time, which is not desirable because it can lead to defects and loss of throughput.

If, as shown in FIG. 6, the target value will be reached at different times for different substrates, the polishing rate can be adjusted upwardly or downwardly, such that the substrates would reach the target value (and thus target thickness) closer to the same time than without such adjustment, e.g., at approximately the same time, or would have closer to the same value (and thus same thickness), at the target time than without such adjustment, e.g., approximately the same value (and thus approximately the same thickness).

Thus, in the example of FIG. 6, commencing at a time T0, at least one polishing parameter for the second substrate is modified so that the polishing rate of the second substrate is increased (and as a result the slope of the trace 220 is increased). As a result both substrates would reach the target value (and thus the target thickness) at approximately the same time (or if polishing of both substrates halt at the same time, both substrates will end with approximately the same thickness).

The reference substrate can be, for example, a predetermined substrate, or a substrate having the earliest or latest projected endpoint time of the substrates. The earliest time is equivalent to the substrate with the thinnest layer if polishing is halted at the same time. Likewise, the latest time is equivalent to the substrate with the thickest layer if polishing is halted at the same time.

For each of the adjustable substrates, a desired slope for the trace can be calculated such that the adjustable substrate reaches the target value at the same time as the reference substrate. For example, the desired slope SD can be calculated from (V−I)=SD*(TE−T0), where I is the value (calculated from the linear function fit to the sequence of values) at time T0 polishing parameter is to be changed, Vis the target value, and TE is the calculated expected endpoint time.

In some implementations, there is no reference substrate. For example, the expected endpoint time TE′ can be a predetermined time, e.g., set by the user prior to the polishing process, or can be calculated from an average or other combination of the expected endpoint times of two or more substrate (as calculated by projecting the lines for various substrates to the target value) from one or more substrates. In this implementation, the desired slopes are calculated substantially as discussed above (using the expected endpoint time TE′ rather than TE), although the desired slope for the first substrate must also be calculated, e.g., the desired slope SD can be calculated from (V−I)=SD*(TE′−T0).

In some implementations, (which can also be combined with the implementation shown in FIG. 6), there are different target values for different substrates. This permits the creation of a deliberate but controllable non-uniform thickness between substrates. The target values can be entered by user, e.g., using an input device on the controller.

For any of the above methods described above, the polishing rate is adjusted to bring the slope of trace closer to the desired slope. The polishing rates can be adjusted by, for example, increasing or decreasing the pressure in a corresponding chamber of a carrier head. The change in polishing rate can be assumed to be directly proportional to the change in pressure, e.g., a simple Prestonian model. For example, for each substrate, where the substrate was polished with a pressure Pold prior to the time T0, a new pressure Pnew to apply after time T0 can be calculated as Pnew=Pold*(SD/S), where S is the slope of the line prior to time T0 and SD is the desired slope.

The process of determining projected times that the substrates will reach the target thickness, and adjusting the polishing rates, can be performed just once during the polishing process, e.g., at a specified time, e.g., 40 to 60% through the expected polishing time, or performed multiple times during the polishing process, e.g., every thirty to sixty seconds. At a subsequent time during the polishing process, the rates can again be adjusted, if appropriate. During the polishing process, changes in the polishing rates can be made only a few times, such as four, three, two or only one time. The adjustment can be made near the beginning, at the middle or toward the end of the polishing process.

Polishing continues after the polishing rates have been adjusted, e.g., after time T0, and the optical monitoring system continues to collect spectra and determine values for each substrate.

Referring to FIG. 7, in some implementations, one or more of the sequences 210, 220 of values 212, 222 can be used to determine a polishing endpoint. In some implementations, separate endpoints are detected for the substrates 10 a, 10 b, and polishing is halted independently for the substrates (by removal of pressure). For example, the endpoint for the first substrate 10 a can detected as the time T1 at which the function 214 equals a target value TV, and the endpoint for the second substrate 10 a can detected as the time T2 at which the function 214 equals the target value TV.

In some implementations, polishing is halted simultaneously for the substrates 10 a, 10 b. For example, polishing can be halted for both substrates at time T1, at time T2, at the earlier of the times T1 and T2, at the later of the times T1 or T1, or at an average of the times T1 and T2. If a polishing parameter is adjusted during the polishing operation, then a function that is fit to the portion of the sequence after the parameter was adjusted can be used.

It is possible to generate a sequence of values for different zones of the substrate, and use the sequences from different zones to adjust the pressure applied in the chambers of the carrier head to provide more uniform polishing, e.g., using techniques described in U.S. application Ser. No. 13/096,777, incorporated herein by reference (in general, the value can be substituted for the index value to use similar techniques). In some implementations, the sequence of values is used to adjust the polishing rate of one or more zones of a substrate, but another in-situ monitoring system or technique is used to detect the polishing endpoint.

Referring to FIG. 8, a summary flow chart 600 is illustrated. A plurality of substrates are positioned against the same polishing pad by their respective carrier heads (step 602). An in-situ monitoring system makes an initial measurement of each substrate to generate a starting value for each substrate (step 604). Either an adjusted pressure or a delay time is calculated for at least one of the substrate based on the starting values (step 606). Then plurality of substrates are polished with the same polishing pad in a polishing apparatus (step 608), using the adjusted pressure or delay time as described above.

During this polishing operation, each substrate has its polishing rate controllable independently of the other substrates by an independently variable polishing parameter, e.g., the pressure applied by a chamber in carrier head. During the polishing operation, the substrates are monitored as described above to generate a sequence of values for each substrate (step 610). For each substrate, a function e.g., a linear function is fit to the sequence of values for that substrate (step 612). Expected endpoint times that the functions will reach a target value is determined, e.g., by linear interpolation of the linear function (step 614). If needed, one or more polishing parameters for the substrates are adjusted to adjust the polishing rate of that substrate such that the plurality of substrates have closer endpoint conditions (step 616), e.g., such that the plurality of substrates reach the target thickness at approximately the same time or such that the plurality of substrates have approximately the same thickness (or a target thickness) at the target time. Polishing, monitoring and generating the sequences of values continues after the parameters are adjusted, and for each substrate a function, e.g., a linear function, is fit to the values generated after the change of the polishing parameters (step 618). The endpoint conditions are detected for each substrate based on the sequence of values for that substrate (step 620), e.g., at the time where the function for the substrate equals a target value.

The controller 190 can include a central processing unit (CPU) 192, a memory 194, and support circuits 196, e.g., input/output circuitry, power supplies, clock circuits, cache, and the like. In addition to receiving signals from the optical monitoring system 160 (and any other endpoint detection system 180), the controller 190 can be connected to the polishing apparatus 100 to control the polishing parameters, e.g., the various rotational rates of the platen(s) and carrier head(s) and pressure(s) applied by the carrier head. The memory is connected to the CPU 192. The memory, or computable readable medium, can be one ore more readily available memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or other form of digital storage. In addition, although illustrated as a single computer, the controller 190 could be a distributed system, e.g., including multiple independently operating processors and memories.

Embodiments of the invention and all of the functional operations described in this specification can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structural means disclosed in this specification and structural equivalents thereof, or in combinations of them. Embodiments of the invention can be implemented as one or more computer program products, i.e., one or more computer programs tangibly embodied in a machine-readable storage media, for execution by, or to control the operation of, data processing apparatus, e.g., a programmable processor, a computer, or multiple processors or computers. A computer program (also known as a program, software, software application, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file. A program can be stored in a portion of a file that holds other programs or data, in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub-programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.

The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit).

The above described polishing apparatus and methods can be applied in a variety of polishing systems. Either the polishing pad, or the carrier heads, or both can move to provide relative motion between the polishing surface and the substrate. For example, the platen may orbit rather than rotate. The polishing pad can be a circular (or some other shape) pad secured to the platen. Some aspects of the endpoint detection system may be applicable to linear polishing systems, e.g., where the polishing pad is a continuous or a reel-to-reel belt that moves linearly. The polishing layer can be a standard (for example, polyurethane with or without fillers) polishing material, a soft material, or a fixed-abrasive material. Terms of relative positioning are used; it should be understood that the polishing surface and substrate can be held in a vertical orientation or some other orientation.

Particular embodiments of the invention have been described. Other embodiments are within the scope of the following claims. 

What is claimed is:
 1. A polishing method, comprising: positioning a first substrate and a second substrate in contact with the same polishing pad; prior to commencement of polishing and while the first substrate and second substrate are in contact with the polishing pad, generating from an in-situ monitoring system a first starting value and a second starting value from the first substrate and the second substrate, respectively; calculating an adjusted first pressure for the first substrate; polishing the first substrate on the polishing pad with the adjusted pressure and polishing the second substrate on the polishing pad with a second pressure; monitoring the first substrate and the second substrate during polishing with the in-situ monitoring system to generate a first sequence of values for the first substrate and a second sequence of values for the second substrate; and at least one of detecting a polishing endpoint for the first substrate and the second substrate or determining an adjustment for a polishing parameter based on the first sequence of values and the second sequence of values.
 2. The method of claim 1, wherein calculating the adjusted first pressure comprises a default pressure multiplied by a ratio based on the first starting value and the second starting value.
 3. The method of claim 2, wherein the default pressure is a preset pressure or a pressure dynamically calculated based on monitoring of a prior substrate.
 4. The method of claim 2, wherein calculating the adjusted first pressure P_(ADJ1) comprises calculating P_(ADJ1)=P_(DEF1)*(TV−V2)/(TV−V1), where TV is a target value, V1 is the first starting value, V2 is the second starting value, and P_(DEF1) is the default pressure.
 5. The method of claim 4, comprising detecting the polishing endpoint.
 6. The method of claim 5, wherein detecting the polishing endpoint comprises fitting a first function to the first sequence of values and determining a time at which the first function equals the target value, or fitting a second function to the second sequence of values and determining a time at which the second function equals the target value.
 7. The method of claim 1, wherein the in-situ monitoring system comprises an eddy current monitoring system, and wherein polishing the first substrate comprises polishing a first metal layer on the first substrate and polishing the second substrate comprises polishing a second metal layer on the second substrate.
 8. The method of claim 1, wherein the in-situ monitoring system comprises a spectrographic monitoring system, and wherein polishing the first substrate comprises polishing a first dielectric layer on the first substrate and polishing the second substrate comprises polishing a second dielectric layer on the second substrate.
 9. The method of claim 1, wherein the first substrate is the substrate having a thicker layer to be polished.
 10. The method of claim 1, wherein the first substrate is the substrate having a thinner layer to be polished.
 11. A polishing method, comprising: positioning a first substrate and a second substrate in contact with the same polishing pad; prior to commencement of polishing and while the first substrate and second substrate are in contact with the polishing pad, generating from an in-situ monitoring system a first starting value and a second starting value from the first substrate and the second substrate, respectively; calculating a delay time for the second substrate based on the first starting value and the second starting value; polishing the first substrate on the polishing pad; after the delay time from commencing polishing of the first substrate, polishing the second substrate on the polishing pad; monitoring the first substrate and the second substrate during polishing with the in-situ monitoring system to generate a first sequence of values for the first substrate and a second sequence of values for the second substrate; and at least one of detecting a polishing endpoint for the first substrate and the second substrate or determining an adjustment for a polishing parameter based on the first sequence of values and the second sequence of values.
 12. The method of claim 11, wherein calculating the delay time comprises a difference between the first starting value and the second starting value divided by a default polishing rate.
 13. The method of claim 12, wherein the default polishing rate is a preset polishing rate or a polishing rate dynamically calculated based on monitoring of a prior substrate.
 14. The method of claim 12, wherein calculating the delay time comprises calculating ΔT=(V2−V1)/R, where V1 is the first starting value, V2 is the second starting value, and R is the default polishing rate.
 15. The method of claim 14, comprising detecting the polishing endpoint.
 16. The method of claim 15, wherein detecting the polishing endpoint comprises fitting a first function to the first sequence of values and determining a time at which the first function equals the target value, or fitting a second function to the second sequence of values and determining a time at which the second function equals a target value.
 17. The method of claim 11, wherein the in-situ monitoring system comprises an eddy current monitoring system, and wherein polishing the first substrate comprises polishing a first metal layer on the first substrate and polishing the second substrate comprises polishing a second metal layer on the second substrate.
 18. The method of claim 11, wherein the in-situ monitoring system comprises an spectrographic monitoring system, and wherein polishing the first substrate comprises polishing a first dielectric layer on the first substrate and polishing the second substrate comprises polishing a second dielectric layer on the second substrate.
 19. The method of claim 1, wherein the second substrate is the substrate having a thinner layer to be polished. 